Sealed magnetic contact device



y 1967 H- s. WOODHEAD ETAL 3,329,914

SEALED MAGNETIC CONTACT DEVICE Filed Feb. 25, 1966 United States Patent 3,329,914 SEALED MAGNETIC CONTACT DEVICE Harry Stanley Woodhead, Herbert John Sloley, and William Kelly Waugh, London, England, assignors to International Standard Electric Corporation, New York, N.Y., a corporation of Delaware Filed Feb. 25, 1966, Ser. No. 530,212 Claims priority, application Great Britain, Feb. 26, 1965, 8,355/ 65 4 Claims. (Cl. 335-154) The invention relates to a sealed magnetic contact device for use, in cooperation with an electromagnet not part of the device, as a relay, and commonly known as a reed switch.

One form of reed switch with which the invention is particularly concerned consists of a small glass bulb, which may typically be some mm. in diameter and about 20 mm. long, into one end of which are sealed a pair of bars of magnetisable material one of which carries a fixed contact and the other a movable contact on a spring-loaded armature. A magnetic field operates the armature against its spring-loading. The reason that both the bars are of magnetisable material is to facilitate sealing into the glass; the two bars are initially the legs of a hairpin-shaped piece of Wire of one of the well known glass-sealing ferromagnetic alloys, the loop of the hairpin being subsequently removed.

A difiiculty with this form of reed switch is that a longitudinally applied magnetising force establishes useless leakage fiux along the armature support limb. This acts as a magnetic shunt to the contact gap. It is desirable to reduce to a minimum magnetic leakage paths shunting the air gap between the armature and the fixed contact bar, while also reducing the direct air gaps to a minimum. Problems are also encountered in connection with bounce between the contacts, which calls for careful consideration of the spring and armature design.

According to the present invention there is provided a sealed magnetic contact device having two stationary, generally parallel, bars of magnetisable metal sealed through one end of a vessel, a fixed contact provided adjacent the end of one of the bars within the vessel, and an armature carrying a contact for cooperation with the fixed contact mounted by spring means from spacing means of magnetisable metal secured by an interposing member of non-magnetic material to the other one of tlie bars, the last mentioned bar terminating within the vessel short of the vicinity of the contacts.

An embodiment of the invention will be described with reference to the accompanying drawings in which:

FIG. 1 is a view of a complete device of the invention;

FIG. 2 is a longitudinal section through the contact end of the device of FIG. 1 on a greatly enlarged scale; and

FIG. 3 is an end view of the device looking in the direction of the arrows in FIG. 2.

Two bars, 1 and 2, of ferromagnetic alloy sealing readily to glass, are sealed into one end of an elongated glass vessel 3, closed at its other end. The bar 1 has an area adjacent its end plated with palladium to form a fixed contact 4. The other bar 2 is terminated short of the vicinity of the contact 4, but has butt-joined to it an extension piece 5 of non-magnetic copper-nickel alloy. This extension piece forms an interposing member be- 3,329,914 Patented July 4, 1967 tween the bar 2 and a spacing means 6 of magnetisa-ble material in the form of a long spacer 7 of ferromagnetic material and a short spacer 8, of the same material, superposed on one end to form a step. A double leaf spring 9 of an alloy marketed under the trade name Vimetal is welded at one end on top of the spacer 8 and carries, welded to the same side and slightly spaced from the spacer 8, an armature 10. The armature overlays the spacer 7 and is spaced from it the minimum distance allowable for movement of the armature and extends underneath the fixed contact, as viewed in the drawing. Opposite the fixed contact the armature is plated with similar contact metal to that providing the fixed contact. The contact end of the assembly is supported within the vessel 3 by means of a snubber 12.

In a physical embodiment of the switch described above, the bars 1 and 2 were made from 0.047 inch diameter wire, the fixed contact member being 0.55 inch long within the envelope 3 and having an end portion 11 of reduced thickness 0.020 inch thick. The bar 2 terminated at the commencement of this reduced portion. The armature 10 was a strip of ferromagnetic alloy 0.204 inch long, 0.090 inch wide and 0.012 inch thick, while each of the leaves of the spring 9 were 0.225 inch long, 0.087 inch wide and 0.002 inch thick, with the effective length of the spring, between welds, 0.210 inch. The gap between spacer 8 and armature 10 was 0.015 inch and that between the armature and spacer 7 was 0.008 inch.

With embodiments as described above, a total magnetic pull of at least 12 grams or more was obtained, while a pull-off force of 6 grams minimum was provided by the spring. The spring arrangement, coupled with a light armature of sufiicient cross-section to avoid magnetic saturation, resulted in operate times, including bounce, of less than 1.5 milliseconds.

It is to be understood that the foregoing description of specific examples of this invention is not to be considered as a limitation on its scope.

What we claim is:

1. A sealed magnetic contact device having two stationary, generally parallel, bars of magnetizable metal sealed through one end only of a vessel which is closed at its other end, a fixed contact provided adjacent the end of one of the bars within the vessel, an armature carrying a movable contact for cooperation with the fixed contact, a spring fastened by one end to said armature, and spacing meansof magnetizable metal secured betwen said springand an inter-posing member of non-magnetic material, said member of non-magnetic material secured between the spacing means .and the other one of the bars, the last mentioned bar terminating within the vessel short of the vicinity of the contacts.

2. A device as claimed in claim 1 wherein the said interposing member is of metal butt-joined to the end of the said other one of the bars, the said spacing means is secured to one side of the said other one of the bars, a leaf spring is secured to the spacing means and the armature is secured to the leaf spring so as to overlap the fixed contact.

3. A device as claimed in claim 2 wherein the spacing means is of stepped formation, the leaf spring being secured to the step so that the armature is spaced from the other part of the spacing means.

4 4. A device as claimed in claim 3 wherein the fixed 3,170,053 2/1965 Scheidig 200-87 contact is provided by an area of contact metal plated On 3,236,965 2/ 1966 Del Bianco et al 200-87 the first mentioned one of the bars and the armature has ,2 8,32 3/19 6 SCflta 200-87 a similarly plated area for the moving Contact. OTHER REFERENCES 5 References Cited Del Bianco: German application No. 1,116,813, Nov. UNITED STATES PATENTS 1961' 2,648,167 8/1953 Ellwood 20() 87 X BERNARD A. GILHEANY, Primary Examiner.

2,969,434 1/1961 McGuire et al 200-87 X 10 J. J. BAKER, R. N. ENVALL, JR., Assistant Examiners. 

1. A SEALED MAGNETIC CONTACT DEVICE HAVING TWO STATIONARY, GENERALLY PARALLEL, BARS OF MAGNETIZABLE METAL SEALED THROUGH ONE END ONLY OF A VESSEL WHICH IS CLOSED AT ITS OTHER END, A FIXED CONTACT PROVIDED ADJACENT THE END OF ONE OF THE BARS WITHIN THE VESSEL, AN ARMATURE CARRYING A MOVABLE CONTACT FOR COOPERATION WITH THE FIXED CONTACT, A SPRING FASTENED BY ONE END TO SAID ARMATURE, AND SPACING MEANS OF MAGNETIZABLE METAL SECURED BETWEEN SAID SPRING AND AN INTERPOSING MEMBER OF NON-MAGNETIC MATERIAL, SAID MEMBER FOR NON-MAGNETIC MATERIAL SECURED BETWEEN THE SPACING MEANS AND THE OTHER ONE OF THE BARS, THE LAST MENTIONED BAR TERMINATING WITHIN THE VESSEL SHORT OF THE VICINITY OF THE CONTACTS. 